Simple Symetrical Amplifier

[Lazy Cat]

Originally Posted by EternaLightWith

I will build this one. (CSA) I wait with abated breath.

Waiting for the CSA's heatsinks, power tests will follow and of course some pics.

[Esperado]

Originally Posted by Lazy Cat

rough calculation shows 10-15 db more open loop gain.

What is the impact on phase margin and curve ?
Sorry to bore-you with those questions, but so many people complaining with evil GNFb, while i always pretended the contrary with fast amps.
Vas is a place where lot of distortion is generated. When you increase its gain, you increase its distortion, But, in the same time, you have a higher ratio of global feedback.
Your listening conclusion, here, confirm my thoughts (and experience).

[Lazy Cat]

Esperado as we are circulating in the same circle of questions, it is obvious that we cannot determine certain parts values just by calculations. I usually calculate initial values by formulas without any sims and later on make fine tuning by measurements and listening tests. For me that works fine, but that doesn't necessary means it is perfect for someone else, it is just optimal for me. Please feel free to assemble next amp after you already tweak Crescendo.
Regards L.C.

P. S. For me spare time is mostly the problem.

[brianco]

Originally Posted by Lazy Cat

Waiting for the CSA's heatsinks, power tests will follow and of course some pics.

@LC:

Can you please advise which heat-sinks you have chosen for this amp?

Many thanks,

Brian

[Esperado]

Originally Posted by Lazy Cat

Please feel free to assemble next amp after you already tweak Crescendo.

Sorry, i'm not the kind of guy to spend time changing over and over my configuration when i'm satisfied by what i have. I prefer to listen to music :-)
I'm working on my multi amped system, for the moment, with digital filtering, and my next amps will be class D for basses, for obvious reasons you understand, including simplicity, power saving, high damping and no negative impact of switching frequency and limited high bandwidth here.
Of course i keep my old /new SSA for trebles and for a while, while i'm interested by any new input to increase my personal knowledge and future work. :-)
Like signature of power devices and global path' decisions in design: it save time. Like your CSS listening improvements experience.
I design the same way than you: calculations then listening tries and tuning. But, when you chose the best ways from scratch, it save time's tweaking.
As i trust your work, i asked your experience to add-it to mine. The main interest in building a new stuff is to acquire more knowledge and share-it.
Sorry to have bother-you with general questions, i can understand we do not have the same interests.

[guitar89]

HI, lazy cat, still remember me ? Due to alot of reason, I couldn't construct my SSA until recently, I finished it and tested Still blur about what update/upgrade on SSA since I leave for a while.

Last time was ruin by AC surge so this time I put 25V regulation on supply rail. It went nicely just some noises appear due to outside factor.

The board is not yet encased, everything is anywhere around the area of my work. I also integrated the NTC and it makes it really thermally stable alot But it still suffer from noises from input. I also intergrate a 10pf bypass cap on VAS, could it causing the problem ?

The problem is temporarily solve when I grab the input line with my palm, or if I disconnect the input wire (then I have no sound ) So I hereby come to seek advise from forumers to solve this problem ? (what is this noise/problem called anyway ?)

I also notice your TSSA thread, and i'm interested to build it in my next project. Wanted to try the "lowest part count" TSSA and see how 'nice' it would be ^^

Regards,
Leong.

[Esperado]

Originally Posted by guitar89

The problem is temporarily solve when I grab the input line with my palm, or if I disconnect the input wire

Is the grounds wiring correct everywhere ? Is the shield of the inputs plug connected to the star ground point of the amp?
Is the shield of your input cable well weld ?
Is your source clean ?
If yes, may-be you have some oscillation problems

[guitar89]

my star ground plan is slightly different, the first star point is when 2 trafo secondary ground meet with output, then another star point. Its conplicated to describe in correct way, so I attached my 'semi'-layout. The green star where input signal line attached, black star for input ground line.

Since I modified alot from this original layout I made, I also don't have any nice-look updated layout about my current board. The IPS is remain almost the same, so I modified slightly in the attachment.

As for the input cable, I use very cheap ones during testing (can see from outside 2 wires side by side, thus not shield as all I think) since mine only input wire, not yet put any female mounting/adapter, so I connect by crocodile clip only

Maybe my source is not perfectly clean, but not that noisy at least I know. (achieved better noise level than this before) Does oscillation can be heard ?


Just as the reference, I measured the emitter resistor to get the current consumption. They are stable even with music playing.

For the VAS, without noise it was around 10mA. When noise occur, it went up to 13.5mA.
For IPS (first pair), it rises from 3.85mA to 4.2mA when noise introduced.
I forget to measure OPS though.

Thanks for your reply and help.
Regards,
Leong.

[Lazy Cat]

Originally Posted by guitar89

HI, lazy cat, still remember me ? Due to alot of reason, I couldn't construct my SSA until recently, I finished it and tested Still blur about what update/upgrade on SSA since I leave for a while.

Last time was ruin by AC surge so this time I put 25V regulation on supply rail. It went nicely just some noises appear due to outside factor.

The board is not yet encased, everything is anywhere around the area of my work. I also integrated the NTC and it makes it really thermally stable alot But it still suffer from noises from input. I also intergrate a 10pf bypass cap on VAS, could it causing the problem ?

The problem is temporarily solve when I grab the input line with my palm, or if I disconnect the input wire (then I have no sound ) So I hereby come to seek advise from forumers to solve this problem ? (what is this noise/problem called anyway ?)

I also notice your TSSA thread, and i'm interested to build it in my next project. Wanted to try the "lowest part count" TSSA and see how 'nice' it would be ^^

Regards,
Leong.

Hi Leong

Of course I remember you and I wish you'll successfully build something with SSA in its name.

Look when someone starts to play with the design involving some changes like PCB, some parts etc, it is absolutely necessary to have some gear on your desk like scope, PSU with soft start, serial rail resistors for safe work in initial phase of testing and calibrating, digital rms meters, signal generator.

Simply you have to "see" what is happening on the output and other parts of the circuit as well, to take apropriate measures to eliminate anomalies like oscillations etc.

In your case you definitely have a problem with HF oscillation, which raises the bias current level in certain stages and represent as hiss-noise heard from speakers when connected to the output.

So my advice is to go step by step and each step has to be cleared-understood before proceeding to next one.

Regards, Andrej

P.S. I suggest you to go for VSSA

[Lazy Cat]

Originally Posted by brianco

@LC:

Can you please advise which heat-sinks you have chosen for this amp?

Many thanks,

Brian

SK157 I'm waiting for.